TEPCO has installed the fuel removal cover building on unit 3, but not without some glitches. An inverter that controls power to a braking system for the fuel crane failed and briefly caught fire. After extensive investigation they found that some of the control systems were working improperly causing the controller to have power through it continuously. This caused power cables to heat up leading to a small insulation fire. The damaged parts are to be replaced and at this point TEPCO does not think this problem will significantly delay the fuel removal schedule.
Workers have been seen in photos working on the new refueling floor deck of unit 3, inside the cover building. Earlier reporting showed concerns that the radiation levels in this area would be unsafe. Workers could not be in the area for any extended period of time. It appears that fuel removal work will still be done remotely to reduce worker exposures. Having the ability for workers to be in the cover building as needed for work, maintenance or to directly deal with problems improves the chances of over coming any challenges. TEPCO’s estimates of radiation levels on the refueling floor deck were 1.2 mSv/hr or less.
Work to remove fine debris from the spent fuel pool that had not already been removed using large cranes appears to be underway. This preparatory work may reveal other damage to the fuel assemblies or racks. On earlier reports some had been dislodged or moved from their normal positions. Water analysis done previously didn’t show indications of leaking fuel assemblies. Workers could still discover damaged or difficult to remove fuel assemblies. The worst case scenario is having a damaged fuel assembly lose the internal fuel pellets. If loose fuel pellets were to fall into an unsafe configuration this could cause a criticality accident in the spent fuel pool. Doing this work remotely and in a controlled building reduces the potential for worker exposures or releases to the environment.
Work to remove the spent fuel assemblies is set to begin in the fall of 2018.
A machine translation of TEPCO’s report can be found here.
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